Tiger Salamanders

The Unintended Selection Pressures We Exert

Ryan M.E., Johnson J.R., Fitzpatrick B.M., Lowenstine L.J., Picco A.M., Shaffer H.B. 2012. Lethal Effects of Water Quality on Threatened California Salamanders but Not on Co-Occurring Hybrid Salamanders. Conservation Biology. 27(1):95-102

Fitzpatrick, B.M. and H.B. Shaffer. 2007. Introduction history and habitat variation explain the landscape genetics of hybrid tiger salamanders. Ecological Applications 17(2):598–608.

We all understand that as humans we are constantly exerting selection pressures on many different animals and plants. Because of our over population and consumption, our controlling nature, and our misuse of land we often drive many species to extinction, unintentionally create hybrids, and introduce invasive species. In this paper, the authors struck my interest by discovering a selection pressure that we exert that was not really known to occur. Before explaining the paper, I’ll give you a brief history on the topic.

There are a few different types of tiger salamanders that live across Canada and the USA. The current situation in California in particular is a terrifying one. Since the introduction of Barred Tiger Salamanders (Ambystoma tigrinum mavortium) 50 years ago, the native California Tiger Salamanders (Ambystoma californiense) have been in trouble (Fitzpatrick and Shaffer 2007). Not only do the invasive species out-compete the native one, but when interbreeding occurs the hybrid out-compete both parent species.

                                             A is the California Tiger Salamander, B is the Barred Tiger Salamander, and C is the hybrid.                                           Photo  Source: http://www.ispyanimals.com/2012/01/hybrids-good-bad-and-really-ugly.html

This paper initially was looking at the effects of habitat alterations on the native California tiger salamanders and the hybrid salamander (California and Barred tiger salamander offspring). They did a series of tests to see if recruitment of native or hybrid salamander differed when the concentrations of hybrid to native salamanders were altered, and if these differences were affected by the pond type (i.e. seasonal or perennial). During these tests, which lasted about 6 weeks, a major die-off of the larva occurred in 4 out of 6 ponds. This was an unexpected discovery, and the authors were intrigued by it. During these die offs they found that all of the native salamander larva died, but only 56% of the hybrid larva died. This is a great example of hybrid vigour, and shows that the hybrids are more fit. It wasn’t just the salamanders that were affected by these die-offs either, all the invertebrates in the ponds also died, and a significant increase in algae and cyanobacteria production was seen. The authors then looked into the use of pesticides around each of the ponds to see if they could have caused the major die-offs.  They found recent use of the pesticides near the ponds but they could not directly link the die-offs seen during the experiment to the use of these pesticides. This could be an example of another way in which we are exerting selection pressures on these native salamanders. As if they didn’t have enough to deal with.

Another reason this paper stuck out while browsing the Conservation Biology Journal articles, is because last year during Animal Behaviour when we had to write a proposal for a project, I wanted to look into the effects of pesticides and hormones in water on the frequencies of cannibalistic and normal morphs of the blotched tiger salamanders in BC. This gives an indication that water quality does directly affect these animals, and further studies should be done to see exactly what those affects are.